Core B will be in charge of several functions supporting the 5 individual projects. Measurements of mobilization of cells in living tissue will be obtained in order to evaluate the velocity by which primitive cells migrate from the site of storage to areas of damage and promote cardiac repair. This approach will also allow us to establish under normal conditions how the activation of surface receptors on primitive cells evokes a locomotion effect and/or a growth response. The information to be obtained by two-photon microscopy will be complemented with immunocytochemical analysis of cells and myocardium by traditional confocal microscopy. In this manner, the translocated cells will be characterized in terms of expression of stem cell surface antigens, myocyte specific transcription factors, surface receptors and cytoplasmic proteins. Morphometric analysis, which is one of the functions of Core B, will be utilized to determine the absolute number of cardiac stem cells, cardiac progenitors, myocyte progenitors and myocyte precursors in various anatomical regions of the heart. Myocyte volume and number of hearts treated in different manners will be measured. Finally, this Core will provide histologic sections for all projects of the program.